if I wanted to use the 12 pin cd changer aux input on the back of my head unit and connect an mp3 player to it or gaming system, is my only option the nearly $100 auxiliary input adapter made by soundgate? or can I simply get an adapter harness/cable that is that 12 pin harness on one side and RCA type connections on the other? if not, is there any cheaper alternative to hooking up an external audio source such as an mp3 player or gaming system to the back of my bose HU or the cd changer input which is not being used as I don't have a cd-changer...?